A. Substantives and adjectives of the third declension have their genitive in is. The terminations of the nominative are numerous, some ending in one of the vowels a, e, i, o, y, and others in one of the consonants c, (d), l, n, r, s, t, x. This declension comprises nouns of every gender.
Nouns ending in a, e, i, y, c, l,1 and t are neuter.
Nouns in o, or, os, and eus are generally masculine, but sometimes of other genders.
Those in as, aus, es, is, ys, bs, ns, and ps are generally feminine, sometimes masculine.
G. From the paradigms of this lesson it will be perceived, that substantives of this declension vary considerably as to the manner, in which they assume the characteristic termination of the genitive. The following rules are intended to give the learner some insight into the extent of this variation.5
Nouns in a change a into atis, as poēma, poēmatis, n., a poem.
Nouns in e change e into is, as cubīle, cubīlis, n., a couch.
Those in i6 are generally indeclinable, but sometimes have itos, as hydromeli, hydromelitos, n., mead.
Those in y add os, as misy, misyos, n., vitriol.
O commonly becomes ōnis, as sermō, sermōnis, m., speech. But do and go become dinis and ginis, as grandō, grandinis, f., hail; origō, originis, f., origin.7
Nouns in c, d, l, n simply add is, as hālec, hālecis, n. & f., a sort of pickle; David, Davidis, m., a man's name; cubital, cubitālis, n., a cushion; rēn, rēnis, m., the kidney.7
Those in ar, er, or, and ur commonly add likewise is, as nectar, nectaris, n., nectar; ānser, ānseris, m., a goose; lector, lectōris, m., a reader; sulphur, sulphuris, n., sulphur.9
Those in as generally change as into ātis, as vēritās, vēritātis, f., truth.10
The only nouns in aes are aes, n., brass, and praes, m., bondsman, which have aeris and praedis.
Nouns in aus have audis, as laus, laudis, f., praise; fraus, fraudis, f., fraud.
Those in es generally change es into is, as famēs, famis, f., hunger; rūpēs, rūpis, f., a rock; but sometimes into ēdis, ītis, or eris as hērēs, hērēdis, m., an heir; mīles, mīlitis, m., a soldier; Ceres, Cereris, f., the goddess Ceres.
Nouns in is have commonly is, as apis, is, f., a bee; ovis, is, f., a sheep; but sometimes also eris, inis, ītis, or idis, as pulvis, pulveris. m., dust; sanguis, sanguinis, m., blood; lapis, lapidis, m., a stone; Quiris, Quirītis, m., a Roman.—Sēmis, m., one half, has sēmissis.
Those in os change os into ōtis, as sacerdōs, -ōtis, m., a priest; nepōs, -ōtis, m., a grandson; but also into ōdis, ōis and oris, as custōs, -ōdis, m., a keeper; hērōs, -ōis, m., a hero; rōs, rōris, m., dew.11
The termination us becomes oris, eris, uris, ūdis (ūtis), or odis, as corpus, -oris, n., a body; opus, -eris, n., a word; crūs, crūris, n., the leg; incūs, -ūdis, f., an anvil; salūs, -ūtis, f., safety; tripūs, -odis, m., a tripod.
Greek nouns in eus have eos, as Orpheus, Orpheos, &c.
Nouns in ls, ns, and rs change s into tis or dis, as puls, -tis, f., a sort of pap; pars, -tis, f., a part; glāns, -dis, f., any kernel-fruit; sepēns, -tis, f., a serpent.
Those in bs, ps, and ms have bis, pis, and mis, as urbs, -bis, f., a city; stirps, -pis, m. & f., offspring; hiems, hiems, f., winter.12
The only nouns in t are caput, capitis, m., the head, and its compounds, occiput, -itis, &c.
Nouns in x change this letter into cis or gis, as vox, vōcis, f., the voice; calix, calicis, m., a cup; rēx, rēgis, m., a king; cōdex, cōdicis, m., a book.—But nix, f., snow, has nivis; nox, f., night, noctis; senex, adj, old, senis or senicis; and supellex, f., furniture, supellectilis.
1 Nouns in l are generally neuter, but sometimes masculine. 2 Nouns which are sometimes masculine and sometimes feminine, according to the context, are said to be of the common gender. So adolēscēns and juvenis, m. & f., a young man or woman; conjūx, m. & f., a husband or a wife; īnfāns, m. & f., an infant; and a number of others. Nouns of which the gender is unsettled are said to be of the doubtful gender; as diēs, m. & f., a day; penus, m., f., & n., provisions. 3 Neuters ending in e, al and ar have ī in the ablative instead of e; as mare, marī; animal, animālī; calcar, calcārī. Except sāl, far, baccar, jubar, hēpar, and nectar, which retain the e. 4 Prepositions before their cases are not accented. 5 These rules, though not directly connected with the exercises of this lesson, are yet recommended to the careful attention of the student. 6 Nouns in i and y are Greek, and so are their genitives itos and yos. 7 A number of other nouns in o have likewise inis, as homō, a man; nēmō, nobody; Apollō, &c.—Carō, flesh, f., has carnis, and Aniō, m., the name of a river, Antēnis. 8 But lac, n., milk, has lactis, and those in men have minis, as nūmen, nūminis, n., the deity. Greek nouns in on have onis and ontis, as īcon, īconis, f., an image; Acherōn, ontis, m., name of a river. 9 But those in ber and ter have bris and tris, as Octōber, Octōbris; pater, patris, m., a father. Some in ur have oris, as ebur, eboris, n., ivory, &c—Jecur, n., the liver, has jecuris, or jecinoris, and hēpar, n., the liver, hēpatis or hēpatos; cor, n., the heart, has cordis; iter, n., a journey, itineris, and Jūpiter, m., Jovis. 10 Greek nouns in as have antis and adis (or ados, as gīgas, gīgantis, m., a giant; lampas, lampadis or lampados, f., a lamp. other exceptions are: ās, assis, m., a coin; mās, maris, m., a male; vas, vadis, m., a surety, and vās, vāsis, m., a vessel. 11Ōs, n., the mouth, has ōris, but os, n., a bone, has ossis. The genitive of bōs, m. & f., an ox or cow, is bōvis. 12 But the adjective caelebes, single, has caelibis and the compounds of ceps have ipis, as princeps, -ipis, the foremost. The genitive of anceps, doubtful, is ancipitis.